Pump Laser Research Articles

Thermoelectric active cooling for transient hot spots in microprocessors

Modern microprocessor performance is limited by local hot spots induced at high frequency by busy integrated circuit elements such as the clock generator. Locally embedded thermoelectric devices (TEDs) are proposed to perform active cooling whereby thermoelectric effects enhance passive cooling by the Fourier law in removing heat from the hot spot to colder regions. To mitigate transient heating events and improve temperature stability, we propose a novel analytical solution that describes the temperature response of a periodically heated hot spot that is actively cooled by a TED driven electrically at the same frequency. The analytical solution that we present is validated by experimental data from frequency domain thermal reflectance (FDTR) measurements made directly on an actively cooled Si thermoelectric device where the pump laser replicates the transient hot spot. We herein demonstrate a practical method to actively cancel the transient temperature variations on circuit elements with TEDs. This result opens a new path to optimize the design of cooling systems for transient localized hot spots in integrated circuits.

Dynamically stable radiation pressure propulsion of flexible lightsails for interstellar exploration

Meter-scale, submicron-thick lightsail spacecraft, propelled to relativistic velocities via photon pressure using high-power density laser radiation, offer a potentially new route to space exploration within and beyond the solar system, posing substantial challenges for materials science and engineering. We analyze the structural and photonic design of flexible lightsails by developing a mesh-based multiphysics simulator based on linear elastic theory. We observe spin-stabilized flexible lightsail shapes and designs that are immune to shape collapse during acceleration and exhibit beam-riding stability despite deformations caused by photon pressure and thermal expansion. Excitingly, nanophotonic lightsails based on planar silicon nitride membranes patterned with suitable optical metagratings exhibit both mechanically and dynamically stable propulsion along the pump laser axis. These advances suggest that laser-driven acceleration of membrane-like lightsails to the relativistic speeds needed to access interstellar distances is conceptually feasible, and that their fabrication could be achieved by scaling up modern microfabrication technology.

Anisotropic Fourier Heat Conduction and phonon Boltzmann transport equation based simulation of time domain thermo-reflectance experiments

The anisotropic Fourier Heat Conduction Equation (FHCE) and the multidimensional phonon Boltzmann Transport Equation (BTE) were solved numerically in cylindrical coordinates and in time domain to simulate a Time Domain Thermo-Reflectance (TDTR) experimental silicon/aluminum substrate/transducer setup. The out-of-phase response of the probe laser was predicted at various beam offset distances for a pump laser pulse frequency of 80 MHz and modulation frequency of 10 MHz and compared against experimental measurements for a silicon substrate. The isotropic FHCE was also solved for comparison. Results show that the isotropic FHCE with bulk thermal conductivity of 145 W/m/K significantly underpredicts the out-of-phase temperature difference, particularly at smaller beam offsets. With an isotropic thermal conductivity of 105 W/m/K, the computed results match experimental data at smaller beam offsets well, but overpredicts the experimental data at larger beam offsets. An almost-perfect match is obtained by using an anisotropic thermal conductivity wherein the radial (in-plane) thermal conductivity is set to 85 W/m/K and the axial (through-plane) conductivity is set to 130 W/m/K. The multidimensional frequency and polarization dependent phonon BTE is next solved. The BTE results for the out-of-phase temperature difference match experimental observations well at small and intermediate beam offsets, but overpredicts the experimental data at larger beam offsets. FHCE results are fitted to the BTE predictions, and the extracted (best fit) thermal conductivity is found to be 110 W/m/K.

Crystallization-driven tuneable lasing of perylene doped into the nematic liquid crystal

Versatile devices with tunable capabilities for controlling lasing wavelength and intensity are in high demand. Liquid crystals (LCs) exhibit immense potential for such applications, offering fine-tuning possibilities through external factors. On the other hand, laser technology is currently a research hotspot in optoelectronics, and also in practical applications. The recent market introduction of laser television marks a significant stride toward making such advanced technology accessible in every household. In synergy with laser pumping, the LCs unquestionably can be rediscovered. This study presents a comprehensive investigation into the crystallization phenomenon within a host-guest device, compact in size, free from moving parts, and integrating the liquid crystalline (LC) matrix doped with 3,4,9,10-tetra-(3-alcoxy-carbonyl)-perylene (THCP) dye. The focus lies in examining the influence of varying dye concentrations on multicolor fluorescence, lasing behavior, and device morphology. The systematic analysis of Random Lasing (RL) energy thresholds and the impact of DC voltage on light intensity modulation is demonstrated. Morphological changes were monitored in real-time using optical microscopy techniques, including crossed polarizer, and fluorescence imaging under 450 nm excitation. Utilizing advanced Transmission Electron Microscopy (TEM) techniques, we explore exceptional insights into our set of devices, providing novel information about the THCP crystallization process for the first time in the literature. To gain a comprehensive understanding of the crystal forming and molecular geometry we examined additionally the THCP dye, using X-ray diffraction and Raman spectroscopy. Furthermore, we showcase that varying the pumping energy enables multicolor tuning in the fabricated systems, presenting an attractive feature in the context of laser display technologies.

Mid-IR supercontinuum generation in a silicon nitride loaded lithium niobate on sapphire waveguide

In spectroscopy, having access to a wide range of wavelengths within the mid-infrared region is crucial for conducting thorough and versatile analyses. In our research, we successfully demonstrate numerically the generation of supercontinuum within a waveguide made of silicon nitride loaded onto lithium niobate on a sapphire substrate, with a specific focus on the mid-infrared wavelength range. By implementing effective lateral leakage and dispersion engineering techniques, we have significantly broadened our system’s spectral range, covering wavelengths from the near-infrared (near-IR) to the mid-infrared (mid-IR) regions. Our results indicate that when a silicon nitride-loaded lithium niobate waveguide is excited with a commercially available femtosecond fiber laser pump at 2070 nm, it has the capability to produce a supercontinuum that spans more than one octave within the mid-infrared wavelength range.

Engineering chaos in a four-mirror cavity-optomechanics with mechanical drives

We study the occurrence of chaos in a four-mirror optomechanical cavity with mechanical drives externally interacting with two transversely located moving-end mirrors of the cavity. The strong cavity mode, driven by the pump laser, excites mechanical oscillations in both moving-end mirrors with its radiation pressure. These radiation-pressure-induced mechanical effects then lead to the indirect coupling between two transverse mirrors, where intra-cavity field mimics as a spring between two mechanical objects. By computing Poincaré surface of sections for both mirrors over a wide interval of initial conditions, we illustrate the transition from stable to mixed – containing stable islands and chaotic seas – Poincaré surface of sections with external mechanical drives. To further explore the occurrence of chaos with mechanical drives, we measure the spatio-temporal responses of moving-end mirrors initially located in mixed Poincaré sections. We find that both of the mirrors follow chaotic temporal evolution with external mechanical drives, even in the absence of any one of the mechanical drives. To quantitatively measure the occurrence of chaos, we computed the possible Lyapunov exponents and collective Kolmogorov–Sinai Entropy of the system. We find that the largest Lyapunov exponent, and corresponding Kolmogorov–Sinai Entropy, not only gains positive values with increase in external drives but also crucially depends on the initial conditions chosen from the Poincaré surface of sections. Furthermore, we show the enhancement in chaotic dynamics of mirrors in the presence of mechanical damping rates associated with the oscillatory motion of the mirrors.

Fluorescence amplification in laser-pumped random media: Fundamental limitations

Experimental data on the narrowing of fluorescence spectra of laser-pumped random media are interpreted within the framework of a probabilistic model of incoherent amplification of the stimulated component of fluorescence. R6G- and DCM-doped layers of dense-packed anatase and anatase-rutile particles and suspensions of DCM crystallites were examined under pulse-periodic laser pumping with various pump intensities at the wavelength of 532 nm. It was shown that, in the case of quasi-stationary fluorescence response at high pump intensities, amplification of stochastically propagating partial components of fluorescence field at various wavelengths is governed by the pump-independent factor of fluorescence amplification and the average number of stimulated emission acts in the pumped system. Analysis of the experimental data has shown that, despite certain simplifying assumptions, the considered model reasonably describes evolution of the fluorescence spectra of random fluorescent media with the increase in the pump intensity. A procedure of recovery of the fluorescence amplification factor from the sets of fluorescence spectra obtained at various pump intensities is considered. Features of the spectral shapes of the recovered amplification factors caused by the influence of the scattering matrices in pumped media are discussed.

Energy Dissipation Engineering for Widely Tunable (1.2–2.1 µm) Optical Parametric Oscillation in Integrated Chalcogenide Microresonators

AbstractWidely separated optical parametric oscillation (OPO) in an integrated Kerr microresonator offers a compact, highly coherent, and low‐power laser source, accessing previously inaccessible frequencies. Yet, extending the sideband of OPO from telecom to beyond 2 µm is still challenged by competing nonlinear effects and reduced Q factors at these extended wavelengths. In this work, efficient signal‐idler separations reaching 99 THz (1250–2130 nm) are demonstrated with a modest 8.1 mW threshold power, leveraging the heightened nonlinearity of GeSbS chalcogenide glass in the integrated microresonators. By pioneering energy dissipation control via pulley couplers, competing nonlinear phenomena are effectively suppressed, enabling the first demonstration of a widely separated OPO (wOPO) in the anomalous dispersion regime. Moreover, the wOPO features a robust existence region across a variety of device geometries, resilient to microresonator width alterations of up to 300 nm. These findings underscore the potential of integrated microresonators to adeptly bridge the telecom band to the MIR spectrum, achieving this transition with minimal power and controlled nonlinearities, a promising avenue for contemporary integrated photonics platforms utilizing heterogeneously integrated pump lasers.

Fabry-Pérot photothermal interferometry in a hollow-core antiresonant fiber for gas detection in mid-infrared

Hollow-core antiresonant fiber can simultaneously act as a miniature gas cell and the light guidance with broad wavelength range, introducing an powerful tool to photothermal spectrosocpy and sensitive gas detection. Photothermal interferometry (PTI) is a spectroscopic tehcnique that employs an interferometer to finely measure the photothermal signal of trace gas. By splicing the HC-ARF between solid core fibers, a Fabry-Pérot (F-P) cavity is formed and enables PTI with a brief in-line design. However, the previous structure commonly adopted single-mode solid core fibers and might introduce large optical loss due to mode field mismatch, particularly for MIR pump laser. This could lead to significant decrease in sensitivity. Besides, the gas pressure effect on the HC-ARF-based PTI gas sensor had not been fully studied. In this work, we demonstrated the PTI for 13CO2 detection at 4.35 µm by employing an HC-ARF with a 100-µm core. An InF3 multimode fiber was utilized for the efficient delivery of MIR pump beam and successfully enhanced the pump power by a factor of 6.7. The limit of detection was determined to be 0.4 ppb at the integration time of 240 s. Finally, the relationship between gas pressure and photothermal signal was experimentally studied and compared with theoretical results.

Impact of pump-phase noise in PPLN-based optical parametric amplifier and wavelength converter for digital coherent transmission

Wideband signal amplification and optical signal processing with a high gain using an optical parametric amplifier based on a periodically poled LiNbO3 (PPLN) waveguide is attractive for constructing wideband optical fiber networks. We experimentally investigate the transfer characteristics of the phase noise of a pump laser in χ(2)-based optical parametric amplification and wavelength conversion on the basis of second-harmonic-generation and differential-frequency-generation processes. We also evaluate the effect of the transferred phase noise on signal quality in dispersion-unmanaged digital coherent fiber transmission systems. We show that the phase noise is transferred only to the wavelength-converted idler and does not affect the amplified signal even by using a pump laser with a MHz-order linewidth. We also show that the phase noise transferred to the idler light can have a similar impact on signal quality as equalization-enhanced phase noise (EEPN) in digital coherent transmission. The signal penalty including EEPN was evaluated with several pump lasers and at symbol rates of 32, 64, and 96 Gbaud. We also propose a method of using correlated pump lights between a wavelength converter pair to cancel out the transfer of phase noise.

High-power Raman lasing and efficient anti-Stokes generation in mm-sized crystalline disk resonators.

We have previously experimentally observed high-power Stokes and second-order Stokes output from a mm-sized CaF2 disk using stimulated Raman scattering. A pump laser at a wavelength of 1.06 µm was coupled via a tapered fiber to the whispering gallery modes (WGM) of the disk. In this Letter, we extend this work and demonstrate the production of the first anti-Stokes sideband at power levels as high as 60 µW in near continuous-wave (CW) operation. The result is a four-component Raman comb at the output, with a wavelength range covering from 1.023 to 1.14 µm. We discuss the threshold dependence of the observed Raman lines on the crystal orientation and provide experimental validation. These advances enable the use of such mm-sized resonators as compact, efficient sources for terahertz-level frequency modulation.

High-efficiency anti-stokes Raman blue laser in CO2 enables high-luminance RGB laser-driven white light

Stimulated Raman scattering (SRS) is an efficient nonlinear frequency conversion method, enabling simultaneous generation of red, green, and blue (RGB) lasers. In order to synthesize a white light source for laser display by SRS, a 532 nm laser was used as pump source, and high purity gaseous carbon dioxide (CO2) was used as the Raman active medium. First, by optimizing experimental parameters, with an f = 1.5 m focal lens, in 0.8 atm CO2 pumped at 304 mJ, a first-order anti-Stokes (AS1) 495 nm blue laser was achieved, with an energy of 31.9 mJ, peak power of 10.9 MW and conversion efficiency (CE) of 10.5 %. Then, Then, the second-order Stokes light (S2) at 624 nm, residual pump laser (S0) at 532 nm, and AS1 laser were utilized as RGB primary colors. By the variation of pressure below 1 atmosphere (atm), the laser-driven white light (LDWL) with adjustable correlated color temperature (CCT) below 4700 K were simulated. Finally, LDWL up to 2.6 × 1018cd/m2 of a CCT of 3300 K could be synthesized at an RGB power ratio of PR: PG: PB = 0.447:0.094:0.459, resulting in a white light power CE of 44.4 % and luminous efficacy of 113.7 lm/W. In addition, use of the 574 nm yellow Raman light is expected to realize a four-primary (RGBY) laser display scheme with higher Luminance and broader color gamut. Moreover, the feasibility of using a 515 nm Yb: YAG laser as pump source to widen the range of CCT and improve the brightness of LDWL was discussed.

Effects of squeezed vacuum field on force sensing for a dissipative optomechanical system

We investigate the force sensing of a mechanical membrane in a dissipative cavity optomechanical system (OMS) driven by a squeezed vacuum field accompanying a strong pump laser. Specifically, the red-detuned laser exhibits a more significant improvement for force sensing compared to the blue-detuned laser. The optimal phase angle contributes to achieving much better force sensing. When injecting a squeezed vacuum field with appropriate squeezing parameter and squeezing phase, the standard quantum limit of force measurement can be easily beaten. Furthermore, the adverse effects of the increase in environment temperature and mechanical damping can be suppressed, simultaneously. This scheme provides a theoretical basics for force sensing of mechanical membranes in dissipative OMS and has potential applications in force feedback control, precision measurement, and force sensor design.

Phase locking and absolute frequency stabilization of laser sources for a Pr:YSO quantum memory

We propose a scheme to phase lock a quantum-memory control laser, frequency-conversion pump laser, and two-photon source over three octaves in frequency to operate a quantum memory. The absolute frequencies of the laser sources are determined based on a Doppler-free iodine hyperfine transition. The achieved relative frequency instability and uncertainty were ≤1 × 10–12 and 3 × 10–11, respectively, which are below the requirement for operating a Pr:YSO quantum memory. This scheme simplifies the instrumentation of laser sources in a quantum repeater, and increases the reliability of quantum communication systems.

Comparative study of the multiple wavelength lasing of nitrogen ions: the role of vibrational level-dependent photoionization

We report on an optical amplification and energy threshold of the two most prominent emission lines, 391.4 and 427.8 nm, of the cavity-less lasing of nitrogen ions pumped by femtosecond laser pulses. It was found that the two transitions both show optical amplification under a low gas pressure condition, while the 391.4 nm emission is barely amplified under high gas pressure. Moreover, the 427.8 nm emission presents a significant lower pump laser energy threshold and a larger gain factor than the 391.4 nm emission. Numerical simulations based on a three-state coupling model suggest that the smaller ionization Franck–Condon factor from the ground state of N2 to the vibrational level ν = 1 in X2Σ g + state of N2+ favors the formation of population inversion corresponding to the 427.8 nm emission. Meanwhile, the competition between the strong field ionization and excitation induced by the pumping laser requires higher laser intensity to acquire the population inversion for the 391.4 nm radiation, leading to a corresponding larger energy threshold.

Exceeding two octave-spanning supercontinuum generation in integrated As2S3 waveguides pumped by a 2 μm fiber laser

In this work, we demonstrate over two octaves-spanning supercontinuum generation in integrated As2S3 chalcogenide glass waveguides pumped by a 2 μm femtosecond fiber laser. The pump laser provides 182 fs pulses at 50 MHz repetition rate. Through optimization of the waveguide dimensions, a broad supercontinuum spectrum spanning from 0.6 to 2.8 μm was achieved using a 4 μm wide, 5 mm long waveguide with 357 mW coupled pump power. The findings showcase the potential of dispersion engineered, integrated As2S3 photonics for realizing compact, efficient on-chip supercontinuum sources for mid-infrared applications.

Telecom‐Band Spontaneous Parametric Down‐Conversion in AlGaAs‐on‐Insulator Waveguides

AbstractWidespread commercial adoption of telecom‐band quantum key distribution (QKD) will require fully integrated, room‐temperature transmitters. Implementing highly efficient spontaneous parametric down‐conversion (SPDC) on a platform that offers co‐integration of the pump laser has been an outstanding challenge. Here, using such a platform based on AlGaAs‐on‐insulator waveguides, telecom‐band SPDC (and SHG, second harmonic generation) is reported with exceedingly large efficiencies of 26 GHz generated pairs per mW over a 7 THz bandwidth, which would saturate the usable photon‐flux for a 70‐channel wavelength‐multiplexed QKD system at merely 1.7 mW of pump laser power.

Mechanically Actuated Kerr Soliton Microcombs

AbstractMode‐locked ultrashort pulse sources with a repetition rate of up to several tens of gigahertz greatly facilitate versatile photonic applications such as frequency synthesis, metrology, radar, and optical communications. Dissipative Kerr soliton microcombs provide an attractive solution as a broadband, high‐repetition‐rate compact laser system in this context. However, its operation usually requires sophisticated pump laser control to initiate and stabilize the soliton microcombs, particularly in millimeter‐sized ultrahigh‐Q whispering‐gallery resonators. Here, a mechanically actuated soliton microcomb oscillator is realized with a microwave repetition rate of 15 GHz. This enables direct initiation, subsequent long‐term stabilization, and fine tuning of soliton combs without pump laser tunability that is generally required for soliton microcomb operation. The prospects for using this method with a wide range of applications are revealed that will benefit from mechanical soliton actuation such as optical clocks, spectral extension, and dual‐comb spectroscopy.

Controllable nonlinear effects in a hybrid magnonical semiconductor microcavity

We investigate the bistability properties of the magnomechanical system driven by an amplitude-modulated pump laser. The bistable behavior exhibits a characteristic magnon switching pattern. This behavior is studied for different values of system parameters. A distinct indication of energy transfer between the mechanical and magnon modes becomes evident while examining the mechanical displacement spectrum within the system. Further, by appropriately adjusting the system parameters, it is observed that the system in its steady state exhibits entanglement dynamics. These findings imply that this system holds potential applications in highly responsive magnon switches, magnon sensors, and quantum communication platforms.

Non-reciprocal band structures in an exciton–polariton Floquet optical lattice

AbstractPeriodic temporal modulation of Hamiltonians can induce geometrical and topological phenomena in the dynamics of quantum states. Using the interference between two lasers, we demonstrate an off-resonant optical lattice for a polariton condensate with controllable potential depths and nearest-neighbour coupling strength. Temporal modulation is introduced via a gigahertz frequency detuning between pump lasers, creating a polariton ‘conveyor belt’. The breaking of time-reversal symmetry causes band structures to become non-reciprocal and acquire a universal tilt given by Planck’s constant and the frequency of modulation (hΔf). The non-reciprocal tilting is connected to the non-trivial topology of the Floquet–Bloch bands, which have a finite Chern number. Detailed characterization of the lattice potential depth and its dynamics highlights the role of high-energy carriers in the formation of optical potential landscapes for polaritons, demonstrating the possibility of modulation faster than the polariton lifetime and opening a pathway towards Floquet engineering in polariton condensates.